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Date: Sun, 13 May 2018 23:50:10 +0100
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Amir Goldstein <amir73il@gmail.com>
Cc: linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Miklos Szeredi <miklos@szeredi.hu>
Subject: Re: [RFC][PATCH] ovl_create_index(): vfs_mkdir() might succeed
 leaving dentry negative unhashed
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On Sat, May 12, 2018 at 07:49:21AM +0300, Amir Goldstein wrote:

> :-/ this pattern is too nasty to be open codes twice in ovl and
> once in knfsd.
> For ovl, we can hoist this into the ovl_do_mkdir() helper, but
> what filesystems really need is vfs_mkdir_hashed(), then knfsd
> can use it as well.

Not really - handling of that case is really different for different
callers, especially if you look into the "it's managed to disappear
in between ->mkdir and ->lookup" case.  Passing by reference seriously
limits what the callers can do; if it works for overlayfs, more power
to you, but it's not a good general-purpose helper.